The present invention relates to a sealing device for a rotating shaft such as a propelling shaft which is disposed in the water.
In a working ship such as a semisubmercible petroleum boring rig and crane barge, a ship position controlling device is provided for cruising or moving and stopping at a predetermined position on the berth. The controlling device comprises a propelling device disposed in the sea water. In such a propelling device, a shaft, a bearing and all frictionally engaging surfaces are lubricated and cooled by providing a lubricating oil thereto, and a shaft sealing device such as an oil seal is provided for preventing both oil leakage from the propelling shaft and sea water invasion. Also, in such a marine working ship, since the ballasting water must be changed corresponding to the sea condition, weather and working purpose, the propelling device has been often used in water of 6 to 35 m in depth. Generally, if the depth of the propelling device is greatly varied, for example in a large capacity oil tanker, in order to maintain optimum operating conditions for the shaft shielding device the sealing pressure is maintained at 0.5-1.0 kg/cm lower than the sea water pressure at the same level of depth, corresponding to the amount of the ballasting water, by a high-low changeover head tank method for generating a sealing hydraulic pressure.
However, in a marine working ship, the depth of the propelling device is frequently and greatly varied. Therefore, it is impossible to maintain the full function of the sealing device for the propelling device. Thus, there is a great possibility of oil leakage and quick abrasion in the sealing device.